1. Field of the Invention
The present claimed invention relates to the field of encapsulated integrated circuit packages. More specifically, the present claimed invention relates to the reduction of blowholes or voids in molten plastic encapsulated integrated circuit packages which contain bulky heat sinks.
2. Prior Art
In an attempt to remove heat from an integrated circuit die in an integrated circuit package assembly, the integrated circuit die is often placed onto the top surface of a thermally conductive heat sink. Most thermally conductive heat sinks such as, for example, copper or ceramic slugs are extremely bulky. As a result of the bulky size of the heat sink, when the integrated circuit package assembly is inserted into a mold cavity the heat sink occupies a large area in the bottom half of the mold cavity. Thus, when molten mold compound is introduced into the mold cavity, the flow of the molten mold compound in the lower half of the mold cavity is restricted and therefore slowed.
Because the flow of molten material is slowed in the bottom half of the mold cavity, the faster flowing molten mold material in the top half of the mold cavity is able to flow over the top surface of the integrated circuit package assembly before the molten mold compound is able to flow under the mold cavity. As a result, the molten mold material in the top half of the mold cavity reaches and blocks air vents in the mold cavity. Therefore, air under the integrated circuit package assembly is unable to be exhausted through the vent hole and becomes trapped under the integrated circuit package assembly. The trapped air leads to the formation of blowholes or voids in the body of the molded package surrounding the integrated circuit package assembly.
Attempts have been made to alleviate the formation of blowholes or voids. These attempts include forming holes through the die attach paddle of the leadframe and or through the heat sink in order to balance the flow of molten mold material over and under the integrated circuit package assembly. However, these methods require substantial additional machining of the leadframe and the heat sink and dramatically raise the cost of the encapsulated integrated circuit package assembly.
Consequently, a need exists for an integrated circuit package assembly which does not create voids on the body of an encapsulated package, which does not require substantial machining of the heat sink, and which does not dramatically increase the cost of the encapsulated integrated circuit package assembly.